Impact control for impact wrenches

ABSTRACT

A control for impact wrenches and method in which a predetermined number of impacts are delivered after the wrench has applied a predetermined torque.

United States Patent 11 1 Whitaker 14 1 Dec. 25, 1973 IMPACT CONTROL FOR IMPACT [56] References Cited WRENCHES UNITED STATES PATENTS [75] Inventor: George C. Whitaker, Los Altos, 2,261,204 11/1941 Amtsberg 81 /52.3 Calif. 2,342,783 2 1944 Aron et al... 81 5146 x 3,018,866 1/1962 12111011 et al. 81 524 R [73] Asslgneel Sales Engineering Company, 3,464,503 9/1969 Houck 173/20 Redwood City, Calif. [22] Filed: May 11, 1972 Primary Examiner.lames L. Jones, Jr.

An --P 1D. Fl h 1 al. 211 Appl. 190.; 252,492 e r e [57] ABSTRACT [22] U.S. Cl. 81/533, 113/(1) 3 A control for impact wrenches and method in which a E58} F111 01Search.............:111"i;53;52 52, 5 2 .5, predetermined "umber of impacts de'ivered the wrench has applied a predetermined torque.

5 Claims, 3 Drawing Figures l'rn 41 28 2 VALVE RESERVOIR (36 37 3 PRESET 9 COUNTER PATFNTEUUHIZS H173 sum 1 or 2 RESERVOIR PRESET COUNTER IMPACT CONTROL FOR IMPACT WRENCHES BACKGROUND OF THE INVENTION This invention relates generally to impact wrenches and more particularly to a method and apparatus for indirectly controlling the torque delivered by controlling the number of impacts.

Control of torque delivered by an impact wrench has been attempted by various methods. In one method the amount of fluid delivered to a fluid-driven impact wrench is measured and the fluid turned off after delivery of a predetermined amount. In another wrench, the delivery of power to the torque wrench is interrupted when a predetermined torsional resistance is encountered. These methods have not reliably delivered a predetermined torque to a number of successive bolts.

OBJECTS AND SUMMARY OF THE INVENTION It is an object of the present invention to provide an improved control and method for controlling the number of impacts delivered in an impact wrench.

It is another object of the present invention to provide a control and method in which a predetermined number of impacts are delivered after the wrench has delivered a predetermined torque to thereby indirectly control the torque delivered.

It is still a further object of the present invention to provide a control apparatus and method in which the number of impacts delivered to an impact wrench, after a predetermined torque has been reached, is controlled by a preset counter which interrupts the power to the wrench after a preset count is reached.

The foregoing and other objects of the invention are achieved by an impact wrench and method in which means are provided for generating an output signal with each impact of the hammer, counting means receiye and count the output signals, and after a preset number of impacts the power delivered to the wrench is interrupted.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic view, partly in section, showing a fluid-driven impact wrench control system in accordance with the invention. A

FIG. 2 is an enlarged view of the mechanism for generating an output signal for each impact.

FIG. 3 is a schematic view of an electrically driven impact wrench with an impact control system in accordance with the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS A fluid-driven impact wrench is shown in FIG. 1. The wrench comprises a fluid motor 11 which drives the impact wrench 12. The impact wrench is of conventional construction and includes a hammer 13 which is urged towards the impact anvil (not shown) by spring 14. As the motor rotates the ball cam 15, the hammer is moved to compress the spring by acting on balls 16 until the spring is compressed. Thereafter, further rotation brings the elongated slots 17 into cooperative relationship with the balls whereby the hammer can move forward under the force supplied by the spring. The hammer then impacts an anvil which includes camming surfaces to cause the anvil to rotate and drive the shaft 18 and socket 19.

When the motor 11 initially drives the impact wrench, the hammer does not impact since the torsional resistance encountered is not sufficient to cause the ball cam to rotate with respect to the hammer. When the torque increases to a predetermined amount, the ball cam will rotate with respect to the hammer to cam the hammer upwardly and compress the spring 14. The hammer is then released to deliver an impact. The impact action occurs when a predetermined initial torsional resistance is encountered. The predetermined initial torque is set by appropriately selecting the spring constant and/or preloading the spring. This, of course, establishes the predetermined or initial torque applied to an associated bolt prior to the start of the impacting.

I have discovered that the amount of torque delivered to an associated bolt is related to the number of impacts applied after reaching said predetermined torque. In accordance with the present invention, means are provided for presetting the number of impacts applied after reaching the predetermined initial torque. Referring to FIGS. 1 and 2, means are shown for stopping the delivery of fluid to the motor 11 after a predetermined number of impacts. Means cooperate with the hammer for generating an electrical signal each time the hammer moves to compress the spring. Referring particularly to the figures, there is provided a support block 21 mounted on the housing 22. The support block 21 and housing 22 are suitably threaded to receive barrel 23 which includes spring-loaded plunger 24 which bears against the ball 26 to urge it against the seat 27. When the ball is in seated position, it protrudes within the housing near the top edge 27 of the hammer. The plunger 24 includes an enlarged end which is adapted to form one stop for the spring 20 and a retaining ring 33 mounted in the barrel cooperates to retain the opposite end of the spring. As the hammer moves upwardly, the cam surface 28 strikes the ball and urges it to the position shown by dotted line 29. The other end of the plunger is adapted to bear against the arm 31 of switch 32. I

When the plunger is moved outwardly, it operates the switch 32 which applies a signal to the preset counter 36. The signal may be a voltage from battery 37 applied to the preset counter each time the switch is closed.

The preset counter may be an electronic or electromechanical counter which can be reset to zero and which counts the number of impulses applied. The preset counter may, for example, be a Series 7102 counter manufactured by Veeder-Root. Such a counter counts and displays the total number of impacts and provides an output signal when the preset number of impacts is achieved. When the preset number, preset by knob 38, is reached, an output signal is generated on the lines 39. In the embodiment of FIG. 1, the line 39 is connected to a solenoid-operated valve 41 which controls the application of fluid to the fluid motor along the line 42.

In its deenergized condition, the valve allows fluid.

under pressure to flow directly through the flow regulator 43 to the fluid motor. When a voltage appears on line 39, the valve is activated and the fluid shunted through the bypass line 44 to return to the fluid reservoir 46. The trigger 47 of the impact wrench controls the fluid flow to the wrench. When it is operated, it operates reset switch 48 returning the counter to zero count. The valve is deenergized allowing valve 41 to again connect the pump 45 through regulator 43 to the fluid motor 11.

To vary the RPM in order to obtain a finer torque setting, the system is equipped with the flow regulator 43.

The regulator regulates the flow of fluid to the impact wrench or, in other words, controls the gallons per minute delivered. As the flow is reduced, the RPM is reduced.

In certain instances it is desirable to operate the wrench as a straight impact wrench. Override switch 51 provides means for operation as a conventional impact wrench. When it is open, the'valve 41 is deenergized to continuously supply fluid from the pump to the motor. The wrench may also be electrically driven such as illustrated in FIG. 3 in which a motor 56 drives a gear box 57 which drives the impact wrench mechanism. The preset counter in this instance serves to control relay 58 which when energized opens the switch 59 to stop delivery of power. The speed can be controlled by use of an autotransformer 61.

Again, by presetting the counter, the impact wrench 57 delivers a predetermined number of impacts after having reached its predetermined torque and thereafter is stopped assuring that a constant torque is applied to each bolt with which the wrench is associated.

Thus, it is seen that the wrench has a counting device to count impacts which are sensed by an electromechanical sensor. The counter can be preset to a given number whereby when the number of impacts is reached, power to the wrench is interrupted. It is possible to vary the force applied with each impact by varying the spring tension on the impact mechanism. This, of course, will also determine the predetermined torque prior to beginning of impacting and can be used in connection with the electronic counter and RPM control to achieve and deliver accurate torque to associated equipment.

I claim:

1. An impact wrench of the type having a movable impact hammer, means causing said hammer to impact after a predetermined torque has been delivered, means cooperating with said hammer for generating a count signal each time the hammer impacts, preset counter means for receiving said count signal and providing a count of the impacts and an output signal when a preset count is reached, means for presetting said counter means whereby when a selected count is reached said counter means delivers said output signal, and means responsive to said output signals for interrupting further application of power to said impact wrench.

2. An impact wrench as in claim 1 wherein said means for generating a count signal comprises an electrical switch and means cooperating with said hammer for operating said switch as the hammer is moved.

3. An impact wrench as in claim 1 wherein said impact wrench is driven by a fluid motor and said means for interrupting application of power to said motor interrupts the flow of fluid to said motor.

4. An impact wrench as in claim 1 wherein said impact wrench is driven by an electric motor and said means for interrupting application of power to said motor interrupts the electrical power to said electric motor.

5. An impact wrench as in claim 1 including means for disabling said impact control means whereby the wrench can be operated as a conventional impact wrench. 

1. An impact wrench of the type having a movable impact hammer, means causing said hammer to impact after a predetermined torque has been delivered, means cooperating with said hammer for generating a count signal each time the hammer impacts, preset counter means for receiving said count signal and providing a count of the impacts and an output signal when a preset count is reached, means for presetting said counter means whereby when a selected count is reached said counter means delivers said output signal, and means responsive to said output signals for interrupting further application of power to said impact wrench.
 2. An impact wrench as in claim 1 wherein said means for generating a count signal comprises an electrical switch and means cooperating with said hammer for operating said switch as the hammer is moved.
 3. An impact wrench as in claim 1 wherein said impact wrench is driven by a fluid motor and said means for interrupting application of power to said motor interrupts the flow of fluid to said motor.
 4. An impact wrench as in claim 1 wherein said impact wrench is driven by an electric motor and said means for interrupting application of power to said motor interrupts the electrical power to said electric motor.
 5. An impact wrench as in claim 1 including means for disabling said impact control means whereby the wrench can be operated as a conventional impact wrench. 